That would be Dean's insistence on fiscal conservatism and balanced budgets.
Now, I don't want to put forth the idea that I believe in wasteful public spending, because I do not. However, according to Keynesian economic theory expanded into the thoughts and theories of the likes of John Kenneth Galbraith, it is sometimes beneficial for the government to run a deficit.
For instance, while I'm certain we can all agree that Bush's military Keynesian spending will do little to propel long-term economic stability, insistence on a balanced budget may not be the answer either. In its 2003 report card, the American Society of Civil Engineers gave the US a D+ in infrastructure (
http://www.asce.org/reportcard/). If you click on the link, you will see that the total needed costs over 5 years to renovate the nation's infrastructure are in the neighborhood of $1.6 trillion.
Now, investing in infrastructure needs would be a wonderful economic stimulus. The state of disrepair of our infrastructure indirectly costs us billions of dollars annually. If the public sector were to fund a massive rehabilitation and rebuilding project over a decade, it would undoubtedly result in budget deficits over the short term. However, the deficits would likely result in an overall stimulus, albeit a lagging one, as more people were put to work. Furthermore, the long-term benefits would be tremendous, as not only would people and business not have to deal with the shortcomings of dilapidated infrastructure, but they would directly benefit for many years from the infrastructure itself.
By insisting on balanced budgets, the Democrats will be failing just as much as the Republicans in meeting the real challenges that face us on the domestic front. The key is framing the argument in a way that highlights the wastefulness of Republican deficits while simultaneously imprinting the overall benefits of increased infrastructure spending.